Conventionally, there has been known an accumulator including a housing that includes an injection opening into which pressure gas is injected, and a gas plug as a gas plug that occludes the injection opening. In this accumulator, the gas plug is fixed to the housing by welding so that the pressure gas is sealed in the housing.
An accumulator according to a conventional example will be described with reference to FIGS. 5A to 6B. FIGS. 5A and 6A are schematic cross-sectional views illustrating a gas plug 350 according to the conventional example. FIGS. 5B and 6B are views illustrating a state where the gas plug 350 according to the conventional example is welded, and are enlarged cross-sectional views illustrating the vicinity of an injection opening 112b of a housing 110.
As illustrated in FIG. 5A, the gas plug 350 according to the conventional example is made of metal, and has a welding portion 351 on a lower surface 350a of the gas plug 350. The gas plug 350 is welded to the housing 110 by melting the welding portion 351 in a state where the welding portion 351 is making contact with the housing 110. In such a configuration, as illustrated in FIG. 5B, because the welded gas plug 350 protrudes from the housing 110, an overall length of the accumulator 100 is extended.
Therefore, due to a demand for downsizing the accumulator 100, as illustrated in FIG. 6B, there has been proposed a configuration including a concave portion to which the gas plug 350 occluding the injection opening 112b is fitted (e.g., Patent Literature 1). Owing to such a configuration, the size of the accumulator 100 as a whole can be reduced when compared with the configuration not including the concave portion, as illustrated in FIG. 5B, since the gas plug 350 does not protrude from the housing 110.
According to the configuration illustrated in FIGS. 6A and 6B, the gas plug 350 is welded to the housing 110 by melting the welding portion 351 in a state where the welding portion 351 is making contact with a bottom surface 110a of the concave portion. When the welding portion 351 is melted, an outer peripheral portion of the gas plug 350 may be deformed, such as being expanded. Therefore, it is essential that a space S is provided between an inner peripheral surface 110b of the concave portion of the housing 110 and the gas plug 350 in a state where the gas plug 350 is fitted to the concave portion.
In such a configuration, there may be a case, depending on a usage environment of the accumulator 100, where a foreign matter, such as water or dust, enters the space S. Particularly, when water or other liquids (e.g., engine oil, brake fluid, suspension fluid, and the like) are collected in the space S, surface processing, such as plating, paint and the like, of individual members may be affected. As a result, rust and the like may be formed on the surfaces of the gas plug or the housing, and a problem, such as degradation of the strengths of those members, may arise.